1. Field of the Invention
This invention pertains generally to entropy coding in video compression, and more particularly to quantization parameter adaptive coefficient scanning in video compression.
2. Description of Related Art
Advanced video coding, such as H.264/AVC, can utilize both spatial and temporal predictions to increase coding gain. Producing an efficient encoded video bitstream generally involves an encoder performing block partitioning, prediction, transforms, quantization, coefficient scanning and entropy encoding. Decoding of encoded video by a decoder is performed substantially in the reverse process.
The process of converting the two-dimensional (2D) block of transform coefficients into a one-dimensional (1D) signal, involves executing a process according to a scanning pattern, followed by a coding process, such as run-length coding, to make the resulting encoded video signal stream more compact. During scanning it is preferable that the larger, more significant, coefficients are scanned at the beginning of the sequence so as to be more efficiently coded in the encoded video.
Traditional H.264/AVC scanning is performed according to a fixed scanning pattern, such as discrete cosine transforms (DCT) in a zigzag scanning pattern starting from the lowest frequency coefficient (DC) to the highest frequency coefficient. Alternatively, adaptive scanning is utilized such as described with mode-dependent directional transforms (MDDT). In certain forms of adaptive scanning, the scanning pattern is initialized based on the intra prediction mode and then an algorithm applied at both encoder and decoder to update the scanning patterns.
However, each of these approaches provide a limited coding efficiency.
Accordingly, there is a need for more efficient video coding processes. The present invention fulfills that need and overcomes shortcomings of previous coding techniques and their associated coefficient scanning mechanisms.